Hexagonal boron nitride nanosheets as metal-free electrochemical catalysts for oxygen reduction reactions

A high-performance ball milling technique was developed for synthesizing hexagonal boron nitride (h-BN) carbon paper (CP) electrodes as metal-free catalyst for the oxygen reduction reaction (ORR) and hydrogen storage (electrochemically) in acidic media. The h-BN nanosheets were functionalized with glycine to enhance the number of active sites and to boost the catalytic activity. The ball-milled h-BN catalytic electrodes demonstrated ultra-high catalytic activity toward electrochemical hydrogen adsorption/desorption (～3.5 times higher than pristine electrodes) as well as ORR in acidic electrolytes. Furthermore, in-situ durability analysis of the h-BN electrodes was performed via conducting a long-duration cycling experiment (>200 cycles). A mechanistic reaction pathway (sequential) including chemisorption and charge transfer reactions (four-electron and two-electron pathways) was also proposed for the ORR. Considering superior catalytic activity of as-prepared h-BN/CP electrodes, this class of metal-free nanostructured materials can be employed as inexpensive catalysts for the electrochemical H-storage and ORR within various energy storage/conversion devices (e.g., batteries, electrolyzers, and fuel cells).